Spain's Garbine Muguruza returns the ball during a quarter finals match against Venus Williams of the United States at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Gregorio Borgia)

Venus Williams serves the ball during a quarter finals match against Spain's Garbine Muguruza at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Gregorio Borgia)

Venus Williams, of the United States, returns the ball during a quarter finals match against Spain's Garbine Muguruza at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Gregorio Borgia)

Spain's Garbine Muguruza celebrates after winning a point during a quarter finals match against Venus Williams of the United States at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Gregorio Borgia)

Croatia's Marin Cilic returns the ball to John Isner of the United States during their match at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Alessandra Tarantino)

John Isner of the United States returns the ball to Croatia's Marin Cilic during their match at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Alessandra Tarantino)

Rafael Nadal of Spain reacts after winning a game during his match against Dominic Thiem of Austria at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. Thiem beat Nadal 6-4, 6-3. (AP Photo/Alessandra Tarantino)

Rafael Nadal of Spain returns a ball during his match against Dominic Thiem of Austria at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. Thiem beat Nadal 6-4, 6-3. (AP Photo/Alessandra Tarantino)

Rafael Nadal of Spain sweats during his match against Dominic Thiem of Austria at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. Thiem beat Nadal 6-4, 6-3. (AP Photo/Alessandra Tarantino)

Dominic Thiem of Austria celebrates after beating Rafael Nadal of Spain at the Italian Open tennis tournament, in Rome, Friday, May 19, 2017. (AP Photo/Alessandra Tarantino)

ROME (AP) — Rafael Nadal's winning streak ended at 17 matches as he lost in straight sets to Dominic Thiem in the quarterfinals of the Italian Open on Friday.

Venus Williams is also out of the tournament after the American was defeated 6-2, 3-6, 6-2 by third seed Garbine Muguruza of Spain.

The result bodes well for Muguruza's defense of her French Open title.

Thiem's 6-4, 6-3 victory came after he was beaten by the Spaniard in the Madrid Open final last week.

"Of course I came in with a very aggressive game style, because I knew that if I want to have a chance, then I have to do something different and be more aggressive," Thiem said. "I knew that if it goes in, everything, maybe I have a chance. If not, maybe I also lose easy.

"But today was one of these days where I really felt the ball great on the racquet, and a lot of risky shots went in. It was a very, very good performance and I think probably one of my best matches."

The 30-year-old Nadal, who was seeded fourth, had won consecutive clay-court tournaments in Monte Carlo, Barcelona and Madrid and was aiming for an eighth title at the Foro Italico as he prepares for the French Open in less than two weeks.

"I just have to congratulate (Thiem), because he was better than me this afternoon," Nadal said. "He played great in all aspects. Just well done for him.

"It's obvious that I did not play my best match. I have been playing a lot ... so is not easy after playing almost every day for the last four weeks," he said.

Their quarterfinal was postponed by rain, with Djokovic leading 6-1, 1-2, and will resume Saturday.

The 23-year-old Austrian dominated from the start, racing into a 5-1 lead. Nadal recovered and broke back to cut the gap to 5-4 but Thiem needed just one of his two set points when Nadal's backhand down the line landed just wide.

Thiem almost broke again early in the second set but Nadal managed to save two break points and go on to hold his serve.

However, Thiem took advantage on his opponent's next service game, putting in several delightful returns which had the audience on their feet before closing the game with a crosscourt forehand.

Thiem almost allowed Nadal back into the match but managed to cancel out three break points to go into a 5-3 lead and he broke again to take the match when Nadal sent a forehand long.

The other semifinal pits John Isner against No. 16 seed Alexander Zverev.

The unseeded Isner, who hit 21 aces, beat sixth-seeded Marin Cilic 7-6 (3), 2-6, 7-6 (2) in a serve-dominated quarterfinal to become the first American to reach the last four at the Italian Open since Andy Roddick in 2008.

Muguruza raced into a 4-0 lead against Williams, who was seeded ninth, and comfortably closed out the set.

The 36-year-old Williams used her experience to bounce back in the second, although she had to save three break points immediately after earning her first break of the match.

It seemed as if the match was going Williams' way when she broke in the first game of the deciding set but Muguruza broke straight back and earned the double break when the American double-faulted twice.

Muguruza broke again in the final game, sealing it when a Williams forehand down the line landed wide.